Study On The Interaction Of Lipid-coated Quantum Dots With Cells

Compared with conventional organic fluorescent dyes, quantum dots show unique size-dependent optical properties, which make them appealing as a new class of fluorescent probes, and have gained increasing applications in the fields of molecular diagnosis, target therapy,biomedical imaging and biosensor, etc, which promote the evolution of bio-analytical chemistry and biomedical engineering. The following several works have mainly performed by taking the interaction of quantum dots with cells as the line of this dissertation.1. Encapsulation of Quantum Dots in Phospholipid MicellesPhase transfer is an essential and nontrivial step for QDs that render solubility only in nonpolar organic solvents to be useful as biological reporters. In this study hydrophobic QDs were encapsulated with phospholipid and PEG-phospholipid. The abtained micelles were characterized by UV-Visible spectroscopy, fluorescence spectroscopy, fluorescence microscopy imaging and Transmission Electron Microscope, respectively. The results showed that QDs encapsulated in poly(ethylene glycol)-phospholipid micelles with one QD per micelle was more feasible than that encapsulated in phospholipid micelles with many QDs per micelle. The as-prepared water-compatible QDs all hold high photostability and narrow size-distribution.2. Nonspecifical Binding Study of Functional QD Micelles to CellsA major problem for the application of nanoparticles in cellular imaging is that nanoparticles tend to bind nonspecifically to cellular membranes. Based on the first part work, functional QD micelles with chemically reactive groups (e.g., NH2- , COOH-, and CH3-) were prepared by encapsulation of QDs into functional PEG-phospholipid micelles, and their nonspecifical binding to COS-7 cells were investigated by using confocal laser scanning microscopy. The results indicated that nonspecifical binding of QD micelles depended on particle concentration and incubation time. The surface charge of QD micelles and the serum in cell culture medium also affected the nonspecifical binding. In particular, functional QD micelles with highly charged surface groups, such as carboxylic acids and amines, have been shown to more strong nonspecific binding to cells than that with little charged methyl groups. These results offered a foundation for further better biological application of quantum dots in cell biological field by pertinent modification of their surface to minimize nonspecific cellular binding of QDs.3. The Selectively Binding and Cellular Internalization Study of QD-angiogenin ConjugatesAngiogenin is closely correlated with the occurrence and development of cancers. Based on above work, QD-angiogenin conjugates, prepared using an aptamer that bridges the inorganic fluorophores and angiogenin, were employed to recognize target cells. The cellular internalization study of the conjugates was followed. With the function of angiogenin receptor, QD-angiogenin conjugates could be selectively bound to human umbilical vein endothelial cells and human cervical carcinoma cells. Z-axis scanning studies demonstrated that the QD-angiogenin conjugates were internalized to intracellular organelles of target cells. Subcellular localization and fluorescent colocalization studies indicated that the conjugates mainly located in organelle lysosome after entering the cells. The QD-angiogenin conjugates could be potentially utilized as a novel cellular recognition system in the field of tumor angiogenesis, tumor early diagnosis and target therapy.